SFO-LHR in late Oct00:

Fare Basis: WLXUKSPX
"NOTE - THESE FARES ARE NOT UPGRADEABLE THROUGH MILEAGE PLUS/ SYSTEM UPGRADES / SALES UPGRADES TO A HIGHER CLASS OF SERVICE"

Fare Basis: VKXES2
"NOTE - THESE FARES ARE NOT UPGRADEABLE THROUGH MILEAGE PLUS/ SYSTEM UPGRADES / SALES UPGRADES TO A HIGHER CLASS OF SERVICE"

Until recently, both of these fares could be upgraded using systemwides.